This invention relates to a method and apparatus for forming blocks and is particularly concerned with the formation of concrete blocks with a rough surface resembling that of a split face block or having a textured or irregularly smooth surface.
In the manufacture of concrete blocks, blocks are typically formed by the compression of concrete mix in a mold using a combination of pressure and vibration. In a typical manufacturing process, molds are open at the top and bottom and have a retractable bottom plate. Concrete mix is introduced into the mold cavity from the top of the mold and compressed by means of a plate which descends into the mold and forms the top surface of the mold cavity. These plates are typically hydraulically activated and referred to as “stripper shoe plates” or “shoe plates”. Vibration of the mold during compression is used to hasten the compaction and formation of the block. After a brief period of compression, a block is stripped from the mold. During stripping, the mold is raised while the shoe plate holds the block in position on the bottom plate. After the mold has been raised, the shoe plate is raised and the block is released. According to other known processes, rather than raising the mold, the bottom plate is retracted and the shoe plate applies a downward pressure pushing the block though the open bottom of the mold. Both of the described processes render a block with smooth vertical sides. In many applications it is more esthetically desirable to have a block with a rough or irregularly smooth surface.
One method of forming blocks with a rough surface is to form one large block and split it into two small pieces after the concrete has cured. This process renders a product known as split face block. While the appearance of a split face block is preferable to that of a smooth face block in some applications, the splitting process is time consuming and increases the cost of producing blocks for several reasons including the creation of substantial waste material.
A known alternative for forming blocks with a rough surface is to use a mold cavity with projections, protrusions or other obstructions attached to the interior of the mold such that the block is torn, scraped or smeared as the block is stripped from the mold. An example of such a process can be seen in U.S. Pat. No. 5,217,630, issued Jun. 8, 1993. Various styles of projections, protrusions and other obstructions are known in the block forming art. Some known processes also include a lower wall or lip which extends inwardly from the mold wall whereon the projections are attached. Other known processes also include a reinforcing mesh screen in front of the projections. These methods may be cheaper than manually producing a split face block, but produce a block which is generally less esthetically desirable. In addition, the projections, protrusions or other obstructions attached to the interior of the mold may clog with concrete mix, requiring frequent cleaning and resultant down time for machinery.
Another known alternative, an example of which can be seen in U.S. Pat. No. 6,224,815, issued May 1, 2001, uses a mold with two cavities divided by a vertically-oriented member comprising a grate. The action of stripping the blocks from the mold is used to create a roughened surface on the grate side of the blocks.
Another known alternative, an example of which can be seen in U.S. Pat. No. 3,981,953, issued Sep. 21, 1976, is to use a mold with one or more grooved surfaces on the interior of the mold which are at an angle to the direction in which the mold is stripped. Some known processes use wall projections and protrusions in addition to the grooved surfaces.
Another known alternative embeds a frame or pattern within the concrete mix during compaction. The frame is then moved upwards or otherwise relative to the concrete mass such that the portion of the concrete mix above the frame is retained on or about the frame, randomly fracturing the surface of the block.
Another known alternative uses a mold with opposed, inwardly extending upper and lower lips along at least one of the sidewalls of the mold. The upper lip is located at about the determined height of the composite fill level within the mold cavity, and the lower lip is located at the bottom of the mold cavity. During operation, a metal pallet is placed under the mold. Composite material is filled from the open top. The action of stripping the blocks from the mold creates a roughened surface on the lip side or sides of the block. When the blocks are stripped from the mold, the lower lip acts to strip fill retained between the lips of the mold away from the remainder of the block that will become the roughened surface. Another known process uses a mold that has only a lower lip with grooves oriented at an angle to the direction that blocks are stripped from the mold.
In addition to the random, broken appearance of a split face block, it is also desirable to create blocks with an irregular but smooth surface that imitates natural quarried stone. Like the appearance of a split face block, a block with an irregularly smooth appearance can be more esthetically desirable in some applications than that of a smooth face block. A known method for forming a block with an irregularly smooth surface is to use a mold having an interiorly textured mold sidewall that is retractable by means of hydraulic cylinders or otherwise. Concrete mix is introduced into the mold cavity from its open top. The mix is then compacted using a shoe plate, and vibrated to form a concrete block. The textured cavity wall is then retracted away from the block, and the mold is raised while the shoe plate holds the block in place. The shoe plate is then raised to release the block.
A common drawback of many of the previously used methods that attempt to simulate split face blocks or textured face blocks, is that they produce blocks which all have an identical or substantially similar face, rather than the uniquely random look that results in manually split blocks or textured blocks. Additionally, many of the known methods for mass producing split face and textured face blocks employ costly equipment or costly methods.
Thus, there is a need for a device and method for forming split face and textured face blocks that have non-identical faces. Such a device and method that can be cost effectively employed in high volume production is also needed.